ROTATORIA OF THE UNITED STATES. 
331 
Erie; West Twin Lake near Charlevoix, Midi.; Huron River at Ann Arbor, Mich. Hempel (1898) 
records it front waters connected with the Illinois River at Havana. 111. 
In Europe: Dundee, Scotland (Gosse, 1889); Ireland (Glasscott, 1893; Hood, 1895); Wurttem- 
herg, Germany (Bilfinger, 1894) ; Basel. Switzerland (Ternetz, 1892) ; Lake Nurmijarvi in Finland 
(Stenroos, 1898); Galicia, Austro-Hungary (Wierzejski, 1893). 
26. Rattulus mucosus Stokes (pi. x, figs. 86-91). 
Synonyms: Mastigocerca mucosa Stokes (1896); Mastigocerca rectocaudatus Hilgendorf (1898)? 
Distinguishing characters . — This species shares with Rattulus bicristatus Gosse the peculiarity 
of having two well-marked dorsal ridges with a furrow between them. But in II. mucosus Stokes 
the ridges are lower and extend back only to about the middle of the length of the lorica; the 
entire animal is considerably smaller and of a different form and there are many other points of 
difference. Rattulus mucosus bears much resemblance in general form to R. rattus Muller, R. 
carinatus Lamarck, and R. loplioessus Gosse, but the presence of the two ridges distinguishes it at 
once from these. 
External features. — In side view (fig. 87) the body of an adult specimen is broadly oblong, the 
length being little more than twice the depth. The head-sheath is marked off from the remainder 
of the lorica by a slight constriction, most marked on the ventral side. The anterior margin is 
without teeth or spines. On the ventral side there is, when the head is retracted, a deep, narrow, 
longitudinal fold, which looks like a gap (fig. 89), and on the dorsal side there is a slight notch 
between the two ridges. 
The two ridges extend from the anterior edge backward and a little to the left to a point a 
little behind the middle of the lorica (fig. 86). They are not so high as in R. bicristatus Gosse, 
and the furrow between them is not so wide. For this reason the two ridges may appear in side 
view as but a single one (figs. 87. 88), one completely hiding the other, or they may be entirely 
overlooked. They are marked with transverse striations, similar to those of R. bicristatus Gosse. 
In young specimens (fig. 90) the body is narrower behind than in adults and the toe is longer 
in proportion to the length of the body. 
Corona . — The corona bears the usual wreaths of cilia about its outer margin, two small arcs 
at the sides of the mouth, and three antenna-like processes. One of these is dorsal and club-shaped; 
the other two are very slender lateral rods. 
Antenna }. — The dorsal antenna is situated, not within the groove between the ridges, as in 
R. bicristatus Gosse, but to the left of the left ridge. It projects from a rounded depression on the 
left side of this ridge. (This depression, though not the antenna, is indicated in fig. 86.) The 
lateral antennae occupy the usual position on the sides, considerably behind the middle of the lorica. 
Foot . — The foot, of the usual short, conical form, is joined to the body in a more nnsymmet- 
rical manner than usual. The lorica projects far over it on the left side (fig. 86). but not on the 
right. Thus the foot and toe can be bent to the right side (fig. 88), but not to the left. 
Toes . — There is a single, long, main toe, accompanied by three (possibly more) substyles. The 
rudimentary right toe is here hardly distinguishable from the substyles. The main toe is nearly 
straight, and is frequently carried for long periods bent up against the light side (as in fig. 88); 
the animal then swims about as if it had no toe. In a young specimen (fig. 90) the toe is about as 
long as the body; in older specimens it is shorter than the body. 
Internal organs . — These offer nothing of especial interest, except in case of the trophi (fig. 91). 
These are very massive, but the right manubrium has almost disappeared, persisting merely as a 
short, slender rod. The trophi are thus more unsymmetrical than is usual in the genus Rattulus. 
Measurements . — Length of body, 0.18 to 0.20 mm.; of toe, 0.12 to 0.15 mm.; total, 0.30 to 
0.35 mm. 
History . — This species was first described by Stokes, in 1896, as Mastigocerca mucosa. It had 
been observed by various investigators and referred, doubtfully, to Rattulus bicristatus Gosse. 
Thus. Jennings (1894. p. 19) and Kellicott (1897, p. 50) mention finding a species which has two 
ridges, but does not agree with accounts of R. bicristatus Gosse. In addition to the description 
and figure of Stokes, this species has been figured by Jennings (1900 and 1901 ). 
Hilgendorf (1898) describes as Mastigocerca rectocaudatus a species which resembles the 
present one in many respects. Hilgendorf does not mention the two ridges, but says there is a 
